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Replacement of pre-T cell receptor signaling functions by the CD4 coreceptor.

Norment AM, Forbush KA, Nguyen N, Malissen M, Perlmutter RM - J. Exp. Med. (1997)

Bottom Line: However, the biochemical mechanisms governing p56lck activation remain poorly understood.In more mature thymocytes, p56lck is associated with the cytoplasmic domain of the TCR coreceptors CD4 and CD8, and cross-linking of CD4 leads to p56lck activation.We show that this process is dependent upon the ability of the CD4 transgene to bind Lck and on the expression of MHC class II molecules.

View Article: PubMed Central - PubMed

Affiliation: Department of Immunology, University of Washington, Seattle 98195, USA.

ABSTRACT
An important checkpoint in early thymocyte development ensures that only thymocytes with an in-frame T cell receptor for antigen beta (TCR-beta) gene rearrangement will continue to mature. Proper assembly of the TCR-beta chain into the pre-TCR complex delivers signals through the src-family protein tyrosine kinase p56lck that stimulate thymocyte proliferation and differentiation to the CD4+CD8+ stage. However, the biochemical mechanisms governing p56lck activation remain poorly understood. In more mature thymocytes, p56lck is associated with the cytoplasmic domain of the TCR coreceptors CD4 and CD8, and cross-linking of CD4 leads to p56lck activation. To study the effect of synchronously inducing p56lck activation in immature CD4-CD8- thymocytes, we generated mice expressing a CD4 transgene in Rag2-/- thymocytes. Remarkably, without further experimental manipulation, the CD4 transgene drives maturation of Rag2-/- thymocytes in vivo. We show that this process is dependent upon the ability of the CD4 transgene to bind Lck and on the expression of MHC class II molecules. Together these results indicate that binding of MHC class II molecules to CD4 can deliver a biologically relevant, Lck-dependent activation signal to thymocytes in the absence of the TCR-alpha or -beta chain.

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Flow cytometric analysis of thymocytes from CD3ε−/− (left  panel) or CD4 transgene-bearing CD3ε−/− (right panel) littermates. The  percentage of cells in each population is indicated.
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Figure 5: Flow cytometric analysis of thymocytes from CD3ε−/− (left panel) or CD4 transgene-bearing CD3ε−/− (right panel) littermates. The percentage of cells in each population is indicated.

Mentions: Maturation of DN thymocytes ordinarily requires assembly of the pre-TCR complex (6), which is composed of the CD3 chains, the pTÎħ polypeptide, and the TCR-β chain (5, 7, 10–12). Although the CD4/class II interaction in our transgenic animals mimics pre-TCR signaling in Rag2−/− thymocytes (in the absence of a TCR-β chain), it remained plausible that other pre-TCR components, notably the CD3 polypeptides, might be necessary to permit delivery of an Lck-derived signal. To investigate the signaling requirements in this system, we introduced the CD4 transgene into a CD3ε−/− background. As in Rag2−/− mice, thymocytes of CD3ε−/− mice do not mature beyond the DN stage (11). These thymocytes also contain greatly reduced levels of the CD3γ and CD3δ transcripts, an effect ascribed to the presence of the neomycin phosphotransferase cassette within the closely integrated CD3γδε gene cluster (11). Despite high-level expression of the CD4 transgene in CD3ε−/− thymocytes, no appreciable induction of maturation was observed (Fig. 5). We conclude that although CD4 expression can substitute for the TCR-β chain in promoting thymocyte development, this effect requires expression of CD3 polypeptides.


Replacement of pre-T cell receptor signaling functions by the CD4 coreceptor.

Norment AM, Forbush KA, Nguyen N, Malissen M, Perlmutter RM - J. Exp. Med. (1997)

Flow cytometric analysis of thymocytes from CD3ε−/− (left  panel) or CD4 transgene-bearing CD3ε−/− (right panel) littermates. The  percentage of cells in each population is indicated.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2196103&req=5

Figure 5: Flow cytometric analysis of thymocytes from CD3ε−/− (left panel) or CD4 transgene-bearing CD3ε−/− (right panel) littermates. The percentage of cells in each population is indicated.
Mentions: Maturation of DN thymocytes ordinarily requires assembly of the pre-TCR complex (6), which is composed of the CD3 chains, the pTÎħ polypeptide, and the TCR-β chain (5, 7, 10–12). Although the CD4/class II interaction in our transgenic animals mimics pre-TCR signaling in Rag2−/− thymocytes (in the absence of a TCR-β chain), it remained plausible that other pre-TCR components, notably the CD3 polypeptides, might be necessary to permit delivery of an Lck-derived signal. To investigate the signaling requirements in this system, we introduced the CD4 transgene into a CD3ε−/− background. As in Rag2−/− mice, thymocytes of CD3ε−/− mice do not mature beyond the DN stage (11). These thymocytes also contain greatly reduced levels of the CD3γ and CD3δ transcripts, an effect ascribed to the presence of the neomycin phosphotransferase cassette within the closely integrated CD3γδε gene cluster (11). Despite high-level expression of the CD4 transgene in CD3ε−/− thymocytes, no appreciable induction of maturation was observed (Fig. 5). We conclude that although CD4 expression can substitute for the TCR-β chain in promoting thymocyte development, this effect requires expression of CD3 polypeptides.

Bottom Line: However, the biochemical mechanisms governing p56lck activation remain poorly understood.In more mature thymocytes, p56lck is associated with the cytoplasmic domain of the TCR coreceptors CD4 and CD8, and cross-linking of CD4 leads to p56lck activation.We show that this process is dependent upon the ability of the CD4 transgene to bind Lck and on the expression of MHC class II molecules.

View Article: PubMed Central - PubMed

Affiliation: Department of Immunology, University of Washington, Seattle 98195, USA.

ABSTRACT
An important checkpoint in early thymocyte development ensures that only thymocytes with an in-frame T cell receptor for antigen beta (TCR-beta) gene rearrangement will continue to mature. Proper assembly of the TCR-beta chain into the pre-TCR complex delivers signals through the src-family protein tyrosine kinase p56lck that stimulate thymocyte proliferation and differentiation to the CD4+CD8+ stage. However, the biochemical mechanisms governing p56lck activation remain poorly understood. In more mature thymocytes, p56lck is associated with the cytoplasmic domain of the TCR coreceptors CD4 and CD8, and cross-linking of CD4 leads to p56lck activation. To study the effect of synchronously inducing p56lck activation in immature CD4-CD8- thymocytes, we generated mice expressing a CD4 transgene in Rag2-/- thymocytes. Remarkably, without further experimental manipulation, the CD4 transgene drives maturation of Rag2-/- thymocytes in vivo. We show that this process is dependent upon the ability of the CD4 transgene to bind Lck and on the expression of MHC class II molecules. Together these results indicate that binding of MHC class II molecules to CD4 can deliver a biologically relevant, Lck-dependent activation signal to thymocytes in the absence of the TCR-alpha or -beta chain.

Show MeSH
Related in: MedlinePlus